1. Field of the Invention
The present invention relates to a toner for developing electrostatic latent image and, more particularly, to an electrostatic latent-image developing toner for use with a digital-system electrophotographic apparatus.
2. Description of the Prior Art
Analog-system electrophotographic apparatuses, including copying machines, have been in general use such that light from the light source is illuminated onto an original so that the light reflected from the original is directed to the photoconductor to form an electrostatic latent image on the photoconductor. Also, an image-forming apparatus of digital-system in which a toner-containing developer is supplied to an electrostatic latent image produced in dot unit (digital writing) has been in practical use, including digital copying machines and electrophotographic facsimile units in which image formation is made on the basis of image information read by a printer or image reader as used as an output at a computer terminal.
In the image-forming apparatus of digital-system, an electrostatic latent image is formed on the photoconductor in a unit of dot by digital writing by irradiation of light-beam or light-shutter array, and the latent image is subjected to normal or reversal development; then the resulting toner image is transferred onto a recording medium, such as recording paper, then fixed, whereby a recorded image is produced. Therefore, the toner used in such digital system is required to have good dot-reproducibility. In order to meet such requirement, the toner must have good charging stability. That is, it is necessary that the toner should have stable charging properties such that it is not liable to any substantial variation in the quantity of applied charge due to environmental factors, such as changes in humidity and temperature.
Toner, as in a two-component developing system for example, is triboelectrified by contact with a carrier; and in a single-component developing system, toner is triboelectrified by contact with charge giving members, such as blade and sleeve. However, when any toner component deposits on carrier or charge giving members in the course of repetitive development, the triboelectric function of the carrier or charge giving members in relation to the toner will be lowered and, as a result, the amount of charge applied to the toner will be diminished. In order to enhance the charging stability of the toner, therefore, it is necessary that the toner should have good spent resistance in relation to the carrier and charge giving members.